Polyester includes a product, aliphatic polyester such as polylactones, polylactides, lactone-lactide copolymers and the like, obtained by chemical synthesis and biopolyester such as polyhydroxycarboxylic acid and the like produced by microorganisms. The biopolyester and the aliphatic polyester are known as biodegradable plastics.
The polylactones, the polylactides, or the lactone-lactide copolymers can be produced by a direct polycondensation reaction of hydroxycarboxylic acid, by a ring-opening polymerization reaction of lactones or lactides, or by a bacterial biosynthetic reaction.
Allegedly, a synthesis method for polylactones, polylactides, lactone-lactide copolymers or the like by the ring-opening polymerization reaction can easily give a polyester having higher molecular weight and can be higher in a degree of freedom of molecular design in comparison with other synthesis methods.
Various proposals have been made on a ring-opening polymerization method of cyclic ester such as polylactones, polylactides and the like. For example, Patent Literature 1 discloses a method for producing polylactic acid, comprising a ring-opening polymerization of lactide using an alkyl aluminum compound such as triethyl aluminum as a ring-opening polymerization catalyst. Patent Literature 2 discloses a method for producing polylactic acid, comprising adding a condensation product made from aluminum isopropoxide, silicon tetrachloride and tributyl phosphate into a solution containing L-lactide and triethyl aluminum to allow a ring-opening polymerization reaction.